President Obama and Senator Robert Menendez traded sharp words on Thursday over whether Congress should impose new sanctions on Iran while the administration is negotiating with Tehran about its nuclear program, according to two people who witnessed the exchange.

In the course of the argument, which was described as tense but generally respectful, Mr. Obama vowed to veto legislation being drafted by Mr. Menendez, Democrat of New Jersey, and Senator Mark Kirk, Republican of Illinois, that would impose the sanctions before the multiparty talks are set to end this summer....

His exchange with Mr. Menendez occurred near the end of a question-and-answer session after Senator Angus King of Maine — an independent who caucuses with the Democrats — asked for an update to the nuclear talks.

According to one of the senators and another person who was present, the president urged lawmakers to stop pursuing sanctions, saying such a move would undermine his authority and could derail the talks. Mr. Obama also said that such a provocative action could lead international observers to blame the Americans, rather than the Iranians, if the talks collapsed before the June 30 deadline.

The president said he understood the pressures that senators face from donors and others, but he urged the lawmakers to take the long view rather than make a move for short-term political gain, according to the senator. Mr. Menendez, who was seated at a table in front of the podium, stood up and said he took “personal offense.”

Mr. Menendez told the president that he had worked for more than 20 years to curb Iran’s nuclear ambitions and had always been focused on the long-term implications. Mr. Menendez also warned the president that sanctions could not be imposed quickly if Congress waited to act and the talks failed, according to two people who were present.

This is a remarkable exchange. Americans have been debating Iran policy for years, indeed decades, and experts, former officials (including officials of his own administration), and academics often differ on what policies will be most effective in stopping Iran from getting the bomb. But Mr. Obama has no respect for those who differ with him, and attributes those opinions to pressure from donors "and others" and the desire of politicians for "short term political gain." Let’s leave aside just for a moment who those "others" might be; a good guess would be that he meant the government of Israel and groups such as AIPAC. Let’s just stick to "donors" and "short term political gain."

No wonder Sen. Menendez took "personal offense." What does a senior Democrat get from the leader of his party when he spends years working on the Iran file? The accusation that it’s all about politics and campaign cash. Mr. Obama remains unable to respect differing views; at bottom he considers them not only wrong, but corrupt. Mr. Obama was not, of course, addressing Sen. Menendez; he was characterizing all those who might favor additional sanctions on Iran.

Journalists and academics who write about the "tone" of politics in Obama’s Washington should keep this news story in mind. When a president is fundamentally disrespectful of all those who don’t happen to agree with his own views, and sees them as corrupt, it is no wonder that politics in the capital takes on an ugly tone. And remember: Mr. Obama was addressing Democrats here. His views of the opposing party are no doubt even worse.